Various types of nebulizers have been designed for generating a liquid medication aerosol for delivery to a patient's lungs. In designing a medicament nebulizer, a common goal is to produce an aerosol having as droplets which are very small and as uniform as possible. Only the small droplets will remain in suspension to penetrate deep into a patients lungs. Because of their mass and inertia, any larger size droplets inhaled by a patient will tend to collide with and collect on the walls of the respiratory tract before penetrating deep into the lungs. Generally, the medicament must penetrate deep into the lungs to produce the desired therapeutic effect. Medicament which never reaches the effective areas of the lungs is wasted and consequently increases the cost of the treatment.
As a patient inhales through a mouth piece in one common type of nebulizer, ambient air is drawn through a chamber to the patient. Pressurized air also is delivered to the chamber and is directed over a liquid orifice to aspirate and atomize liquid medicament, thereby forming an aerosol. Normally, the aerosol is mixed with the flow of ambient air which the patient inhales. However, the aerosol may be mixed with oxygen or with oxygen enriched air when required by the patient. Various techniques have been used to deliver the liquid to the orifice, to the make the liquid droplets in the aerosol as small as possible and to separate any larger droplets from the aerosol while the droplets remain in the nebulizer.
In one prior art nebulizer design, pressurized atomization air is discharged through an orifice and is deflected to flow over a fluid orifice to aspirate a fluid stream from the orifice and to atomize the fluid into small droplets as the fluid stream is drawn into the stream of atomization air. The droplets will have a range of sizes. The resulting aerosol is mixed with a larger volume flow of ambient air as it is drawn into the patient's lungs when the patient inhales. Various types of deflectors have been used to direct the atomization air over the fluid orifice to aspirate and atomize the fluid. In one nebulizer design, two fluid orifices are provided on diametrically opposite sides of an atomization air orifice. The atomization air is directed against a deflector bar which splits the air flow into two streams, one flowing over each orifice. In another nebulizer design, the atomization air is discharged from an orifice which is concentric with an annular fluid orifice. The atomization air is directed against a rounded or conical deflector to direct the air flow in a radial pattern over the annular fluid orifice. After the liquid is atomized, it is mixed with a larger volume flow of ambient air when the patient inhales. When the patient is not inhaling, the droplets in the aerosol condense on the interior walls of the nebulizer and flow back to the reservoir. Typically, the aerosol is directed either downwardly towards a fluid reservoir or radially outwardly towards the walls of the reservoir and then flows upwardly towards an aerosol outlet. When the aerosol is caused to follow a tortuous flow path in the nebulizer, the larger droplets tend to collide with and condense on the walls of the chamber and flow back to the fluid reservoir.
One problem with certain prior art nebulizer designs is that the fluid will flow to the fluid orifices for atomization only when the nebulizer is held in an upright orientation. As the atomizer is tilted, the fluid flow to the fluid orifice may decrease and the quantity of droplets generated may drop off and eventually cease, and the average size of the droplets may change. When a patient confined to a bed requires respiratory therapy using a nebulizer, it may be necessary to significantly tilt the nebulizer in order to administer the therapy. Also, sometimes younger children may not hold the nebulizer in an upright position while receiving therapy. Even when nebulizers have been designed to permit tilting during use, they often had a significant residual volume of medicament which could not be atomized by the tilted nebulizer.
Some nebulizers use capillary feed for delivering a flow of liquid from a reservoir to the liquid discharge orifice where the liquid is atomized. So long as a portion of the capillary flow passage is submerged in liquid in the reservoir, liquid will tend to flow to the liquid discharge orifice. In one prior art design, the reservoir has a rounded bottom which delivers the liquid to the lower end of a generally tubular capillary flow passage. However, tilting this nebulizer to any significant degree will interrupt liquid flow, since the inlet end of the capillary feed passage will no longer be submerged in the liquid. In another prior art design, the reservoir has a generally flat bottom extending to a circular side wall. A disk is spaced slightly from the bottom and from the side wall to form a disk shaped capillary fluid feed passage. Near the center of the reservoir, the disk shaped passage connects with a tubular shaped capillary fluid feed passage which leads to the liquid discharge orifice. This construction creates a long fluid feed passage with a 90.degree. bend in the middle. In still another prior art design, an upwardly extending conical capillary passage extends from near a circular side wall of the reservoir to a fluid discharge orifice which surrounds an atomization air orifice. The conical capillary fluid feed passage has a disadvantage in that the upwardly extending conical center in the reservoir limits the capacity of the reservoir unless the size of the reservoir is increased.
Many of the prior art nebulizers are designed to be used only once or a few times and to then be thrown away. The nebulizer design may not lend itself to be easily cleaned so that the nebulizer can be reused.